CHAP. 2. Judicial Control of Powers 301

with felony, when an invalid warrant has been issued, but without
having the warrant in his possession, has no protection. The, Crimi-
nal Justice Act, 1925, s. 44, allows arrest without the warrant being "
in the constable's possession at the time, but this section only applies
where a kwMwarrant has been issued and the Constables Protection
Act does not justify what would apart from the invalid warrant, be an
^unlawful arrest: Horsfeldv. Bfown, [1932] 1 K.B. 355. Th^Custom
and Excise Act, 1952, s. 280, affords revenue officers a considerable
measure of protection where there is probable cause for the seizure
and detention of property as liable to forfeiture.

A public authority (including, with some exceptions, depart- Liability
ments of the Central Government), is, like any other employer,
liable for the wrongful acts of its servants or agents committed in
the course of their employment.1 It was established by the leading
case of Mersey Docks and Harbour Board Trustees v. Gibbs (1866),
L.R. 1 H.L. 93; K. & L. 240, that the liability of a public body whose
servants negligently execute their duties is identical with that of
a private trading company. In spite of the argument that a corpora-
tion should not be liable for a wrongful act, since a wrongful act
must be beyond its lawful powers and therefore not attributable to
it, it is clear that ajspipcu^Qji is, like any other employer, liable for
the torts of its employees acting in the course of their employment
A hospital authority (now a regional hpspital board) will be liable for
negligence in the performance of their professional duties of those
physicians and surgeons who are employed by the authority under a
^^^js£ji^^ equally where the authority employs a specialist
under a contract, not of service, but for services to be rendered by him
as an independent contractor, it is liable to the patient for his negli-
gent treatment: Cassidy v. Minister of Health, [1951] 2 K.B. 343, esp.
at p. 364; cf. Collins v. Hertfordshire County Council, [1947] K.B. 598.
Where, however, the employee's act is vltra vires tie corporation,
there must be express authority from the corporation.2 Those who
are apparently the employees of a public authority are not always
acting in that capacity when committing acts which constitute torts,
They may be acting altogether outside the course of their employ-
ment "on^a frolic of their own." Officials, too, may be acting under
the control of a central authority, even though appointed by a local
authority, or may be performing an independent public duty cast
upon them by the law after their appointment; in neither case is the
employingauthority vicariously ^shl^Stanbiayv. Exeter Corporation^
[1905] 2 KJB. 838, where a local authority was held not liable for the

1 For fuller treatment of this topic, see Dicey, op. «Y.,
pp. 539-41. * ..
* See Winfield, Text-book of the Law of Tort (Sweet & Maxwell), 6th ed.,
pp. 126-8.